As many or a few as you want! Everyone is different and there is no correct amount that will guarantee success! It's not always about the amount of hours you study a day, but how effectively you use those study hours.

As a rule of thumb I would say it's better to study 30 minutes every day rather than 2 hours once a week!

In my opinion I think you will start to progress with 3 lessons a week 🤔

I’ve just started to take classes in italki 3-5 times a week so I have 3h- 5h of serious practice of English and I can see a little difference 😅